This application pertains to the art of electric machine controls and more particularly to electric safety interlock systems for machine enclosures and other guarding.
The invention is particularly applicable to a paper binding machine having a continuously operating conveyor which transports groupings of folded signatures first to an inspection station, then to a binding station, and lastly to a trimmer station, and will be described with particular reference thereto although it will be appreciated that the invention has broader applications such as paint spray systems, parts handling systems, or any other system utilizing a conveyor or the like.
Paper binding machines generally comprise a "assembly line" type mechanical apparatus to produce booklets or magazines from single printed sheets. At the input side, single printed sheets or signatures, are loaded into pockets on feeders. In systems having folded signatures, the feeders supply a continuously operating conveyor with the folded signatures sequentially forming collated gathers which are transported by the conveyor system to an inspection station. A single main motor drive system is utilized to power the entire apparatus including the conveyor, the feeder, the trimmer, and the binder. At each pocket along the conveyor route, an additional signature is stacked on the gather to thus form a booklet.
It is evident, therefore, that it is possible to increase the number of pages for a given booklet by adding feeders having additional pockets and by increasing the length of the conveyor system. It is not uncommon for a paper binding machine to have four modular feeder units each having two signature carrying pockets to produce a booklet comprising thirty-two (32) printed pages.
To ensure operator safety, an enclosure is provided around the feeder units, along with various other guardings around the other moving mechanical parts comprising the paper binding machine. To provide for access into the safety enclosure, maintenance access doors are provided at various strategic locations around the paper binding machine. It has heretofore been the practice to disable the main motor drive upon the opening of any of these maintenance access doors. It has also been the practice to provide a manual override jog button at each of the maintenance doors to enable maintenance personnel to jog the machine and its associated components to determine possible causes of machine malfunction while observing the mechanism while in motion.
One of the problems has been the use of two manual override push buttons by two operators working independently though simultaneously. The problem arises when unbeknownst to a first maintenance personnel, a second maintenance personnel activates the manual override jog pushbutton. The resultant machine motion could, depending upon the circumstances, severely injure the first maintenance personnel who did not request a manual override jog. The danger becomes more pronounced as additional feeders are added to the binding machine to produce a booklet with more pages because the additional associated enclosures further obstruct the view of certain areas surrounding the machine.
The present invention contemplates new and improved electric circuit apparatus and method which overcomes the above-referred problems and others and provides an enclosure safety interlock system which is simple, economical, and fail-safe.